Joni Mitchell's 2002 retirement may be the greatest flounce-out in rock history. She announced her decision to stop making records with a series of impressively bitter interviews. The music industry was "repugnant", "a cesspool" populated by "pornographic pigs" who cared only about "golf and rappers". Furthermore she had "come to hate music" itself. "I hope it all goes down the crapper," she added, cheerily.

It was a spectacular way to hand in your resignation - so spectacular that it seems a shame to spoil it by asking for your job back. Or, worse, going to work for Starbucks: Mitchell's comeback album arrives courtesy of the coffee chain's label Hear Music. Mitchell would probably argue, with some reason, that there's not much difference between a major record label and a fast-food multinational these days, but there's still something a little odd about a woman who complained long and hard about the exploitative nature of the music business (she recently complained of being paid "n-word wages") throwing in her lot with Starbucks, a company that has, over the years, faced a series of charges of unfair labour practice and is currently defending itself against accusations that it engaged in unfair sackings, union-busting and a campaign of surveillance waged by managers on union members. Still, she's not doing anything that peers, including Paul McCartney and Bob Dylan, haven't already done. It makes you wonder which redoubtable 1960s legend will be next to take the Starbucks buck. Van Morrison? Leonard Cohen? Perhaps Neil Young will sign up and offer a version of his anti-corporate anthem This Note's For You, with lyrics amended to suit changing times: "I ain't singin' for Pepsi, I ain't singin' for Coke - in fact, I'm singin' for the deliciously chocolatey Double Mocha Macchiato, handcrafted for you with specially selected ingredients. And can I interest you in a cheese and Marmite panini?"

On the evidence of Shine, what Hear Music offered was artistic freedom. While it certainly isn't "difficult" in the latterday Scott Walker punching-a-side-of-pork-while-screaming-about-Adolf-Eichmann sense of the phrase, neither is it the kind of album that record labels prefer their sexagenarian artists to make these days, in which their "classic" sound is subtly updated and hip young acolytes make guest appearances. The instrumentation is defiantly eccentric: saxophone, piano, the kind of drum machine that would have sounded anachronistic in the early 1980s, pedal steel guitar and washes of synthesized woodwind. The latter occasionally stray worryingly close to Pan Pipe Moods territory. Instrumental opener One Week Last Summer sets the tone of the album - meditative, graceful, becalmed - but there's no getting round the fact that it sounds like something you might hear wafting around the lobby of the Kidderminster Ramada Inn.

Meditative, graceful and becalmed are surprising adjectives, given the prevailing subject matter. Mitchell has said she was provoked out of retirement by the war on terror and looming ecological catastrophe, and a sense of impending doom is never far away. She's hardly the first artist in recent times to make with the End Is Nigh sign, but her response is the diametric opposite of the Arcade Fire's sturm-und-drang or Thom Yorke's anguished finger-pointing. In Hana she suggests we "tackle the beast alone with its tenacious teeth", and there's a sense of fight about the closing rewrite of Rudyard Kipling's If, but more often the tone is not so much one of defiance as a disquieting acceptance of fate. You hear it in the beautiful ballad If I Had A Heart in its chilling refrain of "bad dreams are good in the great plan", and in the echoing drift of the title track, which comes up with a litany of modern-day ills, but never raises its voice in anger.

The sense of an artist roused by the fear that we're all going to hell in a handcart, only to discover that it may be too late and there's nothing we can do to avert disaster, gives much of Shine its emotional heft.

Sanctimony is a condition to which the musical denizens of Laurel Canyon were always prone - in his twenties, Graham Nash was already loftily instructing the world how to Teach their Children - but the urge to wag fingers arises only once. There's a hint of I-told-you-so smugness about revisiting her 1970 eco-anthem Big Yellow Taxi, but that's not the reason the re-recording backfires. Listening to it, you notice there's a sparkiness about the lyric - "they took all the trees, put 'em in a tree museum" - noticeably absent elsewhere: This Place's "money makes the trees come down" suddenly sounds a bit clunky and laboured.

Ultimately, that's a minor quibble in the face of a strange, intoxicating and unsettling album, idiosyncratic enough to make you glad Joni Mitchell put her retirement on hold. Shine is an album worth spoiling the greatest flounce-out in rock history for.